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Sussex Police have contacted 20 people who have reported sexual and physical offences against them by school staff at Ashdown House Preparatory School in Forest Row, East Sussex, police has said. In a statement, a spokesman said:

Arrangements are in hand to interview the others, some of whom live abroad. The investigation continues and now spans a period from the late 1960s to the early 1980s.

The former headmaster of a prep school London mayor Boris Johnson attended has been arrested on suspicion of historic sex assaults.

London mayor Boris Johnson. Credit: Stefan Rousseau/PA Wire

Clive Williams, 69, was also questioned by officers on Wednesday over allegations of child neglect, Press Association sources said. He was the headmaster at Ashdown House Preparatory School in Forest Row, East Sussex, for more than 25 years before leaving in 2003.

A computer and documents have been seized by police investigating the claims against Mr Williams, who was released on police bail and has not been charged.

A Sussex Police spokesman said: "Officers investigating allegations of historic sexual abuse at a school in East Sussex have arrested a local man. The 69-year old was arrested at an address in Barcombe on Wednesday July 9 on suspicion of sexual assaults and child neglect.

"A computer and documentation were seized for examination. After being interviewed, the man was released on police bail on the same day until November 11, while inquiries continue."